Is there a command to order all my ships to group accrodingly and move/attack a given point?
In the "Civilization Manager" screen, click the "Governors" tab. There you can reroute all ships of a given type (I have used this mainly for mobilizing my transports to an unexpected new warzone; I believe they can only be rerouted to a rally point). There you can also multi-change other stuff such as shipbuilding and ( as MarvinKosh replied) colony rally points.
This means it takes painstaking efforts to group vessels and move them manually every turn.
I click "launch all ships" at the beginning of a turn, then I put all lone ships on "guard" (shortcut key "G") or join it into a fleet (select all then shortcut key "F") with a previous guarding ship. Inefficient having idle ships but they can all be moved later as one fleet. Best for constructors because also the starbase upgrade window only needs to open once for the whole fleet.
[EDIT 10 May:] Easier manually, but also easier for older computers which are slowed down by many individual ships with orders.